1. Field of the Invention
This invention relates to a cooling method for a slab-geometry solid state laser medium and laser device which employs that cooling method.
2. Description of the Related Art
Solid state laser media come in two forms, rod and slab-geometry. Rod-geometry solid state laser media are easy to make, but heat from the pumping stage is trapped inside the rod, so that thermally-induced focusing and thermally-induced birefringence occur. In addition, there is the problem that "splitting" of the laser medium occurs.
A slab-geometry solid state laser medium has a larger surface area than a rod-geometry solid state laser medium, so that it dissipates a larger quantity of heat. In addition, in a slab-geometry laser, the laser light advances along a zig-zag path as it is reflected off the upper and lower surfaces of the slab, and as it advances it is amplified. Therefore, even if there is a temperature variation through the thickness of the slab, laser light progresses alternately in opposite directions through a layer of the temperature variation, so that the heat lens effect can be cancelled. Consequently, laser light output from a slab-geometry solid state laser medium has a far superior beam profile to laser light output from a rod-geometry solid state laser medium.
However, even in such a slab-geometry solid state laser medium, when there are temperature variations through the slab in the longitudinal and transverse directions, the beam profile deteriorates. Therefore, it is necessary to make the temperature uniform in both the longitudinal and transverse directions. However since a slab has a very large surface area, it is very difficult to cool it uniformly.